During combustion in a diesel engine, an air/fuel mixture is compressed within a cylinder. Heat generated from compression ignites the air/fuel mixture expanding gases within the cylinder to drive a piston. Exhaust gases are released from the cylinder into an exhaust system.
A diesel particulate filter (DPF) disposed in the exhaust stream filters soot particulates in the exhaust gas. Over time the soot particulates build up inside the DPF. The DPF is periodically cleaned using a regeneration technique that burns the soot particulates.
One conventional regeneration method injects diesel fuel into the cylinder after combustion. Post-combustion injected fuel is expelled from the cylinders with the exhaust gas and is oxidized over catalysts. Heat released during oxidation increases the exhaust gas temperature, which burns trapped soot particulates in the DPF. However, in some circumstances regeneration may generate temperatures that are high enough to damage the DPF causing thermal stress and/or melting.
Various approaches have been employed to limit peak temperatures within the DPF. In one approach, post-combustion injected fuel is limited. However, this approach is ineffective because buildup of soot particulates in the DPF may be sufficient to create an exothermic reaction that increases the temperature.
In another approach, regeneration is performed more frequently to limit the buildup of soot particulates. However, if a vehicle has short driving cycles, the temperature of the exhaust gases may not be high enough to burn the soot particulates. Thus, regeneration may not occur when needed and soot particulates may build up in the DPF.